Investigate timeline scrolling issues

There are a number of issues around scrolling in the timeline that, individually and together, can make for a quite poor experience in certain cases:

- [ ] https://github.com/vector-im/element-web/issues/23208
- [ ] https://github.com/vector-im/element-web/issues/23393
- [ ] https://github.com/vector-im/element-meta/issues/1418
- [ ] https://github.com/vector-im/element-web/issues/8565
- [x] https://github.com/vector-im/element-web/issues/18325

Before engaging in a larger rewrite of the timeline code, we'll need data points on whether or not it's possible to fix these issues with _reasonable_ time investments. Therefore, the idea is to attempt fixes on two of the existing issues under this epic and use the outcome to drive further decision making.

* [ ] https://github.com/matrix-org/matrix-react-sdk/pull/9340 / https://github.com/vector-im/element-web/issues/23393
* [ ] https://github.com/vector-im/element-web/issues/23208

### Time sheeting

Project: `Web: Scrolling`